The present invention relates to an object recognition system which is mounted on a vehicle and determines the relative position of an object ahead of the vehicle, and more particularly to an object recognition system determines the relative position of a vehicle ahead to the vehicle mounting the system.
In recent years, devices which determine the distance and size of an object in front of a vehicle, and which appropriately control the vehicle in accordance with this determination, have been proposed for improving the safety of vehicle operation. A typical method for obtaining information about the object ahead includes the steps of: extracting horizontal edges and vertical edges from captured image; determining whether each of the extracted edges belongs to the object such as a vehicle ahead; and recognizing the object based on the edges determined to belong to the object.
Japanese Patent Application Kokai No. Hei 4-193641 describes an apparatus for determining whether an object existing ahead in the lane of the vehicle mounting the apparatus is an obstacle. The determination is performed according to a guide signal indicating a white line or a state of the road extracted from a captured image by a video camera, and a measurement signal indicating the position of the object measured by a radar apparatus.
Japanese Patent Application Kokai No. Hei 9-178855 describes a method for detecting an obstacle located in the same lane as a vehicle. According to the method, the lane of the vehicle is detected from an image captured by an image sensor, and the position of the obstacle is identified by a radar apparatus. The position of the obstacle is compared with the position of the lane to determine whether the obstacle is located in the same lane as the vehicle.
Furthermore, Japanese Patent Application Kokai No. Hei 10-68777describes an apparatus for detecting the vehicle ahead based on the data indicating the shape of the road derived from an image captured by a camera, and a position signal indicating the position of the vehicle ahead output by a radar apparatus.
However, according to the above conventional methods, the outline or size of an object cannot be recognized correctly because the radar device such as laser type radar only detects he position of the object from a reflective wave from a reflector attached to the object. When the object exists very close to the line defining the lane of the vehicle mounting the radar, the position (direction) of the object can be obtained, but its size cannot be correctly obtained. Accordingly, it is actually difficult to determine whether the object is completely outside the lane of the vehicle, or a part of the object is within the lane of the vehicle. Furthermore, although an object is actually within the lane of the vehicle, it may be erroneously recognized as outside the lane of the vehicle. In addition, when the object enters the lane of the vehicle, or when the object gets out of the lane, the timing of these behaviors of the object cannot be correctly detected because the correct size of the object cannot be obtained.
Accordingly, one object of the present invention is to provide a system, which makes it possible to determine the relative position of an object to the lane of the vehicle based on the size of the object as well as the position of the object.
According to one aspect of the invention, an object recognition system including a radar, an image sensor, and a controller is provided. The radar determines the position of an object, and the image sensor captures an image of the object. The controller sets a processing area within the image captured by the image sensor based on the position of the object determined by the radar and a predetermined size for the object to be recognized. It is preferable that the predetermined size is set to surround the object to be recognized.
The controller extracts edges from the processing area. Extraction of edges can be implemented by detecting a variation of intensity values of pixels contained in the processing area. The edges can comprise horizontal and vertical edges. The controller then recognizes the outline of the object based on the extracted horizontal and vertical edges.
The controller also recognizes lane lines defining the lane in which the vehicle mounting the system of the invention is running. Thus, the relative position of the object to the lane lines is determined based on the recognized outline of the object and the recognized lane lines.
According to one aspect of the invention, the outline of the object can be recognized by determining upper, lower, left, and right ends of the object. Thus, the relative position is determined by comparing the intersections between a horizontal line corresponding to the lower end of the object and the lane lines with the left and right ends of the object. For convenience, the lane lines as well as the ends of the object may be represented by x and y coordinates.
It is preferable that the controller judges whether each of the extracted edges indicates or belongs to the object based on characteristics of the object to be recognized for removing the edges belonging to an object other than the object to be recognized.
According to another aspect of the invention, the upper and lower ends are determined from the horizontal edges, and the left and right ends are determined from the vertical edges.
According to another aspect of the invention, the lane lines are determined by detecting a road area in the captured image. More particularly, intensity values of pixels immediately in front of the vehicle are examined to extract one or more intensity reference values representing the road. Intensity values of pixels within the image are compared with the intensity reference values to detect pixels belonging to the road area. Thus, the road area is detected, and hence the lane lines partitioning the road area are detected.
The controller can comprise a micro-controller which typically includes a central unit (CPU), or a micro-processor, a read-only memory (ROM) containing control programs that when executed by the processor performs respective functions which are to be described hereafter. The controller also includes a random-access memory (RAM) that provides a working area for the CPU and temporary storage for various data and programs.